Defects in magnetic thin films occur at the surface or within the film (in-depth). As the size of modern magnetic devices (such as magnetic read and write heads, recording thin film media and other magnetic sensors) is reduced, the thickness of magnetic thin films is also reduced. Indeed, the thickness of some of the magnetic thin films is approaching the nanoscale range. With increased miniaturization, the influence of nanoscale defects such as voids or dislocations in the magnetic thin films cannot be neglected. Taking the magnetic recording hard disk thin film media as an example, it is known that one of the most important reasons for high error rate of hard disk drives is due to contamination and defects on and in the thin film media. Furthermore, as the thickness of the magnetic layer for the hard disk thin film media decreases to around 10 nm and the average size of magnetic grains decreases to around 7.5 nm, and with an expected increase of the recording areal density of commercial recording disk media up to 10 Gbit/in.sup.2 (1.6 Gbit/cm.sup.2) within five years, the problem of the nanoscale defects within the thin film media will become increasingly significant.
With equipment like the optical microscope and the atomic force microscope (AFM), it is possible to observe and characterize certain surface defects. However, there is still very little development of methods to observe and characterize nanoscale in-depth defects such as voids and dislocations in magnetic thin film, particularly in a fast, easy and non-destructive way. Although the high resolution electron microscope (HRTEM) may be used to analyze the nanoscale structure in thin films and to detect the nanoscale defects in them, sample preparation is tedious and time consuming. Thus, the HRTEM has only limited application to defect detection in magnetic thin film devices manufactured on an industrial production line. Ferrofluid detection may only by used to localize and characterize micron size defects in magnetic thin films. Although, magnetic force microscopy may be used to localize and characterize submicron sized defects in magnetic thin films, the approximate location of each defect must be known beforehand. A media tester may be used together with surface observation equipment to localize submicron indepth defects in the magnetic recording film media. However, this requires a sample which includes a protection overcoat and lubricant layer. In addition, it is difficult to give meaningful information based on the average result over a big area in a short time.
An object of the invention as to provide a way of analyzing defects, especially nano-sized defects, in magnetic thin films which overcomes at least some of the limitations of existing techniques to enable various information about the defects to be gathered efficiently.